This invention relates generally to computer peripheral devices for entry of data into a computer and more particularly to the use of a digitizer for digitizing and entering analog graphic information into a computer.
Often in the use of a computer, it is desirable to input two-dimensional graphic data. A wide variety of devices, commonly known as digitizers, have been proposed for this purpose. A typical form of digitizer is shown in U.S. Pat. No. 3,684,828 to Maher. The digitizer includes a surface for supporting a map, drawing or other source of graphic data, a device for designating points on the surface, and means defining an XY coordinate system for determining the coordinates for each designated point. Interface circuitry is provided for converting the coordinates data into digital numbers in an appropriate communication format for transmission to a computer for further processing. The Maher patent utilizes a piezoelectric substrate to detect the coordinates of the designated points by measuring the surface wave pulses propagating through the substrate surface. U.S. Pat. No. 3,692,936 to Moffitt discloses an acoustic digitizer. U.S. Pat. No. 4,177,354 discloses a digitizer employing a light responsive layer and grid system, used in combination with a light spot emitting stylus to generate digital coordinate signals. The digitizer of U.S. Pat. No. 4,255,617 to Carau et al. employs a cursor with a capacitive pickup in combination with a platen comprising a flat surface within which are embedded two orthogonal grids, each consisting of uniformly spaced individual conductors. U.S. Pat. No. 4,318,096 to Thornburg et al. discloses an XY coordinate tablet which is used in combination with an electrically conductive pen and analog-to-digital converter to provide coordinates data to a computer. It employs a piezoelectric audio pickup which produces a succession of pulses when the stylus is drawn across a textured surface such as a sheet of paper. Such sensors, orthogonally arranged, enable the direction of motion on a surface to be determined and digitized in each access by a bidirectional pulse counter.
All of the foregoing devices, and other similar digitizers provide, for each designated point on the graphic data source, a digital word consisting essentially of the X and Y coordinates of the designated point. As shown in the Maher patent, this information is transmitted in a compatible format to an input port of a digital computer. Such a capability is useful in a variety of tasks in which analog graphic data is input to a computer for subsequent processing. However, such systems are limited in their utility.
For most applications of digitizers, it is desirable for the user to be able to work in an interactive mode, alternately giving instructions to the computer and inputting data points for the computer to process in accordance with the given instructions. Conventionally, this task requires the user to type instructions into the computer through the computer terminal keyboard and then turn to the drafting table to input the data points needed to carry out the instructions. This task is repeated over and over again and can be very time-consuming.
For complex tasks, such as processing bid estimates for the cost of construction of buildings, inputting construction blueprint information from a single source is a severe bottleneck. Consequently, for very large construction projects it is desirable for multiple users to be able simultaneously to input and process data for different parts of the project. Mainframe computers or minicomputers are typically used on a time-shared basis for running programs of this magnitude of complexity. Such machines are limited, however, in the number of input and output devices that can be connected to them. Conventionally, the computer terminal and digitizer each require one I/O port. Moreover, time-shared operation of such systems often leaves an individual user waiting between inputting an instruction and inputting coordinate data while the computer processes data input by other users. Consequently, the use of digitizers has been largely limited to use with stand-alone microcomputers. The latter machines, however, are generally slower and of lesser computing capacity and, therefore, are quickly burdened by computational requirements of manipulation of substantial graphic data.
Various computer system arrangements are known that provide for multiterminal or multidevice access to a computer. U.S. Pat. No. 3,653,001 to Ninke discloses a time-shared computer graphic system, based on a large central processor and having multiple user terminals or local console connected to the processor through modems. Each local console includes a small computer, special purpose display hardware and software, and various local input devices, such as a light pen.
U.S. Pat. No. 4,374,381 to Ng et al. discloses a microcomputer connected to communication ports of a host computer. Connected to the microprocessor are various peripheral devices, such as a keyboard, a bar code reader, a CRT controller with display memory and a CRT with transparent touch pads on its screen.
U.S. Pat. No. 4,078,249 to Lelke et al. discloses a multi-user computer system for formatting textual information, such as in the layout of newspaper advertisements. Each user has a work station which includes a CRT display and keyboard and a graphic digitizer tablet. The keyboard is a standard typewriter style electrical keyboard having keys corresponding to alpha numeric characters and other selected symbols, and a second keyboard in the form of a programmed function keyboard. The display and keyboards of each work station communicate with the computer through an input/output bus controlled by a common logic unit which includes a microprocessor and work station drivers. Digital output signals from the graphic digitizer tablet are relayed back to the host computer, in parallel with communications between the host computer and the keyboard and CRT display portions of the work station. Data input from the graphic digitizer tablet is processed by the host computer and the resultant data is transmitted back through the common logic unit, formatted, and displayed on the CRT of the work station with which the digitizer is associated. This system is typical of and has the drawbacks, discussed above, associated with inputting digitizer data into a host computer in parallel with interactive operation on the data through a CRT display and keyboard. Application of a system like that disclosed by Lelke et al. to much more complicated processing tasks, like bid estimation of construction projects, would require an uneconomical amount of computer processing capacity and provide a slow response time to time-sharing work station users.
Accordingly, a need remains for an improved approach to the inputting of analog coordinate data into a computer for processing in accordance with instructions manipulated by a user of an interactive work station. This need is most acute in relation to time-shared computer systems with multiple user work stations, but also extends to stand-alone or single work station computers, such as microcomputers.